Early diagenetic repartitioning of carbon, sulfur, iron, and manganese in poorly oxygenated to anoxic marine deposits will be studied using new geochemical and stable isotopic data on the Miocene Monterey Formation and the mid-Cretaceous Greenhorn Formation. Our objectives will be 1) to interpret interrela- tionships in the Corg-S-Fe-Mn system in terms of depositional and early diagenetic conditions and 2) to reconstruct the pathways for transfer of sulfur from dissolved and solid inorganic-sulfur species to organic-sulfur compounds in bitumen and kerogen. Organic and inorganic sulfur species will be isolated using a step-wise procedure that will yield seven sulfur fractions (sulphate, elemental, bitumen, acid-volatile, disulfide, barite, and kerogen). Depth and timing of pyrite formation relative to incorporation of sulfur into organic matter will be inferred from the isotopic compositions of the various sulfur fractions in conjunction with the distribution of iron and manganese. The Monterey and Greenhorn both contain interbedded laminated and bioturbated lithofacies that will enable us to sample a wide range of paleoenvironmental and early diagenetic settings. Integration of organic and inorganic sulfur data with manganese and iron data will provide a new basis for interpreting ancient poorly oxygenated to anoxic basins. The geological units selected for this study will permit comparison of sedimentary strata in modern and Miocene coastal upwellings and in modern oceanic and Cretaceous epicontinental settings.
